The present invention relates generally to braking systems, and more particularly to a method and apparatus for selectively disengaging a vehicle drive train from the wheels during wheel lock-up conditions.
Automatic and semi-automatic mechanical transmission (i.e. “AMT”) control systems are known and which are controlled, at least in part, using electronic control systems based on discrete logic circuits and/or software controlled microprocessors. Gear selections and shift decisions are made based upon certain measured and/or calculated parameters known to the control system such as vehicle speed (or transmission output shaft speed), transmission input shaft speed, engine speed, rate of change of vehicle speed, rate of change of engine speed, throttle position, rate of change of throttle position, full depression of the throttle, actuation of the braking mechanism, currently engaged gear ratio, and the like. Examples of such automatic transmission control systems for vehicles are disclosed in U.S. Pat. Nos. 4,361,060; 4,551,802; 4,527,447; 4,425,620; 4,463,427; 4,081,065; 4,073,203; 4,253,348; 4,038,889; 4,226,295; 3,776,048, 4,208,929; 4,039,061; 3,974,720; 3,478,851 and 3,942,393, the disclosures of which are all hereby incorporated by reference.
Similarly, automatic vehicle brake anti-skid or antilock braking systems (ABS) are known. Generally, as locking-up or skidding of a vehicle's wheels occurs, actual or impending wheel lock-up is sensed and the wheels are allowed to roll-up to vehicle speed prior to the vehicle brakes being reapplied. Examples of anti-skid or anti-lock brake systems are described in U.S. Pat. Nos. 3,767,270; 3,768,872; 3,854,556; 3,920,284; 3,929,382; 3,996,267, and 3,995,912, the disclosures of which patents are hereby incorporated by reference. U.S. Pat. No. 4,899,279, also hereby incorporated by reference, discloses vehicle AMT and ABS systems that during actual or impending wheel lock up, the ABS system communicates with the vehicle AMT control system to decouple the vehicle engine, or drive train, from the wheels of the vehicle. Decoupling of the vehicle engine from the wheels reduces the tendency of the inertia of the engine and clutch to hinder the wheels' ability to roll-up to vehicle speed.
While decoupling of a vehicle's engine or drive train from the vehicle's wheels to allow roll-up is beneficial under most circumstances, there are circumstances wherein decoupling can be disadvantageous. For example, if a heavy semi-truck is driven down a steep grade and an impending or actual wheel lock up occurs (as may occur as the result of the engine brake or a loose road surface), decoupling of the vehicle engine from the wheels can be disadvantageous. More specifically, if the wheels of the semi-truck are decoupled from the engine, the truck will momentarily lose the benefit of the engine brake, a situation that can result in the truck lurching forward and/or cause the operator to lose control of the vehicle. Additionally, the disengagement of the clutch removes the resistance to motion provided by the coupling of the driveline with the inertia of the engine. This engine inertia will cause the vehicle to accelerate slower when connected to the driveline. Likewise, this situation can cause the operator to lose control or at least feel uncomfortable when this occurs. The referenced engine may serve as an example of a more general prime mover of the vehicle, a term which encompasses any power plant that provides power to the driveline of the vehicle or other power consuming components of the vehicle. Some examples of prime movers are diesel engines, electric motors, and hybrid power systems.
Therefore, the current invention recognizes the need for a vehicle AMT and ABS system capable of selectively decoupling a vehicle engine from the vehicle wheels, but only under appropriate conditions.
In accordance with the presently disclosed invention(s), the drawbacks of the prior art are minimized by providing a control system, preferably an electronic control system, and a control method, for automatic mechanical transmission systems (AMT's) and antilock braking systems (AB S's) wherein coupling/decoupling of a vehicle engine from the wheels of a vehicle is executed upon measured and/or calculated parameters including, but not limited to, input signals indicative of wheel speed, angle of inclination/declination of the vehicle, operation of the brakes, engine speed, transmission input shaft speed and transmission output shaft speed. Other inputs/parameters, such as signals indicative of throttle or brake positions, rate of change of throttle position or brake positions, condition of the master clutch, currently engaged gear ratio, vehicle mass, vehicle axle configuration (2×4, 2×6, etc.), engine brake power, and the like can also be used to make decisions for control of the AMT and/or ABS systems. The method provides for sensing a wheel lock-up condition, the vehicle status at the time of wheel lockup (vehicle mass, inclination/declination, and the like), and controlling the AMT or ABS in response thereto.
The above is accomplished by providing the electronic control unit with input means for receiving a signal indicative of a wheel lock-up, such as from a vehicle anti-lock brake system and logic to process the input signals to determine the presence or absence of a wheel lock-up condition and the operational status of the vehicle (vehicle mass, inclination/declination, and the like). Upon sensing of a wheel lock-up and vehicle status, e.g., on a steep decline or flat road, the control method causes the vehicle clutch, or other selectively disengagable drive train coupling, to remain engaged to prevent any undesirable forward lurch, or to disengage to allow the wheels to roll-up to vehicle speed. Upon sensing that a wheel lock-up is the result of a vehicle's engine brake, e.g., as may occur as the result of icy or loose road conditions, the control method can cause the ABS to control or modify the vehicle's engine brake. The method further includes sensing termination of wheel lock-up.
In at least one embodiment, the invention takes the form of a method for overriding antilock effects of an antilock braking system on a heavy vehicle, such as a commercial truck, that includes an automatic manual transmission. The method includes detecting a wheel slip event sufficient to initiate an antilock effect from the antilock braking system. Those persons skilled in these arts will understand that examples of such events include a wheel skidding on slippery pavement or slipping on loose gravel, both of which are events that ABS systems normally detect. It is then determined whether or not the heavy vehicle is descending a hill with declination that exceeds a predetermined declination value. If it is determined that the hill is sufficiently steep, initiation of the antilock brake effects will be overridden; that is, braking effect will continue to be applied to the slipping wheels against normal ABS protocol. An important motivation for his procedure is that it would feel abnormal to the driver, with potentially unnerving effects, if braking forces were suddenly removed without notice to the driver while the heavy vehicle is traveling downhill.
The thresholds or predetermined declination values above which ABS procedures are aborted advantageously fall within the range of about five to eight percent, which comprises comparatively steep road grades.
As a compliment to these steps, it is also contemplated that when it is not determined that the vehicle is descending a sufficiently steep hill, ABS prophylactic measures will be allowed to initiate and execute when requisite wheel slippage is detected. This is especially true if the heavy vehicle is traveling on substantially level or flat ground.
Accordingly, the present invention provides an apparatus and method for controlling vehicle AMT and ABS systems to selectively disengage a vehicle engine from a vehicle's wheels under wheel-lock up conditions.